A variety of approaches currently exist for delivering biologically active agents to the CNS and/or the eye. These include, among possible others, oral administration, intravenous-, intramuscular- and transcutaneous administration as well as intra-bulbous injection or application as eye-drops. If the drug is delivered into the systemic circulation, it is being carried to all internal organs and tissues and it has to pass through the blood-brain and/or blood retina barrier (in order to access the CNS and/or the inner parts of the eye). Obviously, all other organs are being exposed to the drug, which may lead to a high incidence of side effects, particularly when the drug exerts its effects on target genes or gene products, which are not specific for the disorder to be treated and/or the target cell or tissue.
Another strategy often employed in brain delivery is the use of invasive methods such as intraventricular infusion systems, intracerebral (polymeric) implants, transplantation of genetically engineered protein-secreting cells and cell implants. These methods are unfortunately only effective for drug delivery to the surface of the brain or to cells immediately adjacent to the depot or infusion site and can be used for example in the treatment of carcinomatous infiltration of the meninges. However, these methods have many limitations because effective drug concentrations in brain parenchyma cannot be achieved.
Like the human central nervous system the human eye is an organ characterized by high complexity and the coordinated functioning of numerous specific structures and tissues. Both are protected by barriers (tear secretion, enzymes, transport mechanisms, blood-retina and blood-CNS barrier) against harmful environmental influences. Like the blood-brain barrier, the blood-retina barrier also represents a physiological barrier for the uptake of medication by the inner part of the eye, and makes pharmacological therapy of ocular diseases very difficult indeed—if at all possible—at the present state of technology.
Medication currently available on the market for the treatment of disorders of the CNS including ophthalmological diseases is therefore almost exclusively available for treatment of clinical symptoms often associated with side effects due to the high doses necessary. A causal therapy of the CNS, and particularly of the back sections of the eye, was not possible apart from the injections. Furthermore, the current state of information on the complex molecular metabolic interrelationship underlying the etiology of retinal diseases of multi-factorial origin is only limited. Consequently, medicaments available on the market are suitable to treat the symptoms of such diseases only.
In view of the need of therapeutic means for the treatment of diseases related to CNS and/or the eye, the technical problem of the present invention is to provide means and methods for the identification and modulation of genes involved in disorders of the CNS and/or the eye. More specifically, the technical problem of present invention is to provide non-invasive methods for the controlled modulation of target genes and gene products in the mammalian CNS and/or eye while overcoming the blood-brain and/or blood retina barrier without injuring it.
The solution to said technical problem is achieved by providing the embodiments characterized in the claims, and described further below.